Embodiments of the present invention relate to transmitting electrical power and communication signals. One of the enabling techniques used in offshore production control systems for hydrocarbon extraction wells, to transmit control and instrumentation signals between topside equipment and subsurface equipment installed on the seabed, is the use of communications-on-power (COP) where communication signals are superimposed on an electrical power signal and transmitted simultaneously with the power signal along a power transmission line in an umbilical cable.
This method is employed to reduce the number of electrical lines needed within the umbilical cable, which provides the main interface between topside and subsurface equipment for hydraulic and electrical power. Using COP eliminates the need for separate power and communication lines within the umbilical cable, thereby reducing its overall cost. However, this technique does have some inherent disadvantages as follows.
At the subsea equipment level there is a need to utilize bulky equipment, such as communications blocking filters and diplexers, to separate and retrieve the communication signals from the power signal and this process can result in electrical noise and transients being generated. These subsea components also consume electrical power
The quality of the electrical power generated topside and transmitted through the umbilical cable may be poor and contain electrical noise and harmonics of the typically 50/60 Hz electrical power frequency and these may interfere with the lower power communication signals which are superimposed on the electrical power signal.
Sudden voltage transients (such as those caused by switching surges or sudden changes to the electrical load) can interfere with the high frequency communication signals. A reduction or elimination of these effects would lead to improvement in the reliability of the communications link and in the overall accuracy of the information transmitted.